The invention relates to a method for indicating the wear of at least one brake pad in a disc brake with an electric motor actuator, a device for performing this method and a corresponding disc brake.
As is known, brake pads are subject to wear. According to vehicle servicing instructions they should be regularly checked and changed after a specific degree of wear, before damage occurs to associated brake parts and a risk of accidents arises due to reduced or non-existent braking performance.
Consequently, hydraulically or pneumatically actuated disc brakes, for example, are equipped with a sensor in the form of a potentiometer, which registers a wear value of the brake pads and transmits this value as a proportional electrical voltage to a higher system. This system has a display, which indicates to the driver in good time when the brake pads are due to be changed. However, the known systems require an additional component for sensing the wear value, namely the sensor. Wear contacts indicating a brake pad wear limit are also known, which have the disadvantage that they need to be replaced when changing the brake pads.
All of these embodiments require additional parts, changing of which generates corresponding additional procurement and fitting costs, especially since brake pads need to be changed relatively often.
Disc brakes in which electric motor actuators act on a clamping device, in order to apply a force to the respective brake pads for a braking sequence, are already known. It is customary with these brakes for the electric motor actuator and/or an adjusting device with an additional adjustment motor to automatically adjust the brake pad as it wears.
The object of the present invention is to improve a method for indicating the wear of at least one brake pad in a disc brake with an electric motor actuator, in which the aforementioned disadvantages no longer occur.
A further object of the invention is to create a device for the method according to the invention, together with a disc brake including this device.
According to the invention, a method is provided for indicating the wear or residual brake pad thickness of at least one brake pad in a disc brake having an electric motor actuator. The method includes the steps of adding the wear adjustment travels of the electric motor actuator and/or of an adjustment motor; and indicating the sum of the wear adjustment travels thus obtained as the wear of the brake pad.
Further according to the invention, a device is provided for indicating the wear of at least one brake pad in a disc brake with an electric motor actuator. The device includes a comparator module for comparing positions of the electric motor actuator and/or of an adjustment motor; an adding module for adding the wear adjustment travels of the electric motor actuator and/or of an adjustment motor; a display module for displaying wear of the brake pad; and a control module for controlling the comparator module, the adding module and the display module and for transmitting control signals for reference adjustments of the electric motor actuator and/or of the adjustment motor to the brake control unit.
Advantageous developments are set forth herein.
It is of particular advantage that the invention does not require any additional sensors or components. An outstanding feature of the method according to the invention is that it uses existing components to determine any wear of brake pads of the disc brake.
It is particularly advantageous if the electric motor actuator of the disc brake, which may also be of the self-energizing type, is used to determine the brake pad wear, since this actuator is designed as a positioning or servomotor, in such a way that the position of its driven shaft is registered in order to control it. These position values are available in an associated brake control unit and can advantageously be used in order to determine any wear of the brake pads.
A method according to the invention for indicating the wear of at least one brake pad in a disc brake with an electric motor actuator comprises the following steps: (i) adding of the wear adjustment travels of the electric motor actuator and/or of an adjustment motor; and (ii) indicating the sum of wear adjustment travels thus obtained as the wear of at least one brake pad.
Where necessary, the wear value(s) may advantageously be transmitted to a higher system (central brake system control/instrument) for further display to the driver. The display is then undertaken by another system (instrument, dashboard) and the brake system supplies the information (for example, via CAN, LIN).
This is particularly advantageous, since in the case of an automatic wear adjustment corresponding values for the adjustment are already available in a higher system, for example in the brake control unit, and can also be evaluated for displaying the wear.
For this purpose, in one embodiment the wear adjustment travel is determined through a position of the electric motor actuator and/or of the adjustment motor. This is especially easy owing to the existence of position values for controlling such a motor. This is easily done by defining the position of the electric motor actuator and/or of the adjustment motor in relation to a reference position. These data values are available in digital form in the brake control unit. They can advantageously be evaluated by simple processing, for example through software instructions.
It is furthermore advantageous that in a preferred development the reference position is assumed at predefined intervals in order to avoid a loss of position. This represents an easy way of confirming or correcting the current position value of the electric motor actuator.
In a further embodiment the wear adjustment travel of the electric motor actuator is determined by the following subroutines:
(1.1) registering of a first position prior to a closing movement of the brake pad;
(1.2) registering of a second position after lifting or return of the brake pad;
(1.3) determination of the wear adjustment travel through comparison of the first position with the second position, the lift or return of the brake pad occurring over a constant travel.
With the aid of the position values for the actuator, it is thereby easy to determine the wear adjustment travel for the wear value. This is particularly advantageous if no suitable value is available for further processing in the brake control unit.
In a preferred embodiment the wear adjustment travel is determined at predefined intervals as a function of a time and/or operating parameter of the disc brake. The wear value can therefore be determined with sufficient continuity over time. In a further development this moreover allows a continuous display of the wear of the brake pad and/or a display for a change of brake pad in step two of the method.
A device according to the invention for indicating the wear of at least one brake pad in a disc brake with an electric motor actuator includes the following: (i) a comparator module for comparing positions of the electric motor actuator and/or of an adjustment motor; (ii) an adding module for adding the wear adjustment travels of the electric motor actuator and/or of an adjustment motor; (iii) a display module for displaying brake pad wear; and (iv) a control module for controlling the comparator module, the adding module and the display module and for transmitting control signals relating to reference adjustments of the electric motor actuator and/or of the adjustment motor to the brake control unit.
In a further embodiment the device has at least one position sensor to provide a reference position for the positions of the electric motor actuator and/or of the adjustment motor. The respective motor can thereby undertake a reference travel to a fixed reference point, which in the closing device, for example, takes the form of a limit switch.
It is advantageous that in a preferred embodiment the comparator module, the adding module and the control module are integral parts of the brake control unit. Since these modules may be embodied as software, they can advantageously be implemented simply without additional components and without additional fitting costs in a brake control unit.
In another development, the electric motor actuator and/or the adjustment motor are equipped with a position-detecting transducer. This caters even for situations in which the actuator and the adjustment motor do not permit precise detection of the position because they are of simple construction. This therefore advantageously extends the sphere of application of the invention.
A disc brake according to the invention with electric motor actuator and indication of the wear of at least one brake pad includes the device according to the invention for performing the method according to the invention.